1. Field of the Invention
The present invention relates to a polarized electromagnetic relay, and in particular to such a relay having an armature extending axially through an opening in a coil body and having a free end moveable between two pole plates disposed at one flange of the coil body.
2. Description of the Prior Art
A polarized electromagnetic relay having a tongue-shaped armature extending axially through an opening in a coil body having opposite spaced flanges is described in U.S. Pat. No. 4,215,329. The relay has a free end disposed at one of the flanges switchable between two pole plates. At least one portion of the pole plates lies flat against the end face of the coil flange and also lies against two spacer members attached to the coil body, which define the spacing between the two pole plates by the thickness of the spacer members. A four-pole permanent magnet arrangement has two poles of opposite plurality disposed against each of the two pole plates.
Using the structure disclosed in aforementioned U.S. Pat. No. 4,215,329, it is possible to construct an extremely small relay having a highly sensitive magnetic circuit. In this known relay, the two pole plates are each angled in three orthogonal planes, with one portion disposed against the coil body at the end face forming pole faces for the permanent magnet, a further portion plugged into the coil body parallel to the coil axis forming the contact surfaces and the working air gap with the armature, and a third portion extending laterally next to the coil body forming a coupling surface with the ferromagnetic housing cap with an interposed foil fixing a defined air gap. This design insures relatively large area contact and pole surfaces for the working air gap, however, the portions plugged into the flange parallel to the coil axis require a corresponding space within the overall structure. For further miniaturization of such a relay, the pole plates should be situated such that the axial length of the relay is enlarged as little as possible.
A similar structure is described in U.S. Pat. No. 4,091,346 wherein two angled pole plates each have one portion disposed flat against the end face of the coil body flange, and each have a further portion extending away from the coil body parallel to the coil axis. The further portions enclose a twopole permanent magnet in the volume therebetween. This permanent magnet is polarized perpendicularly to the coil axis. In this structure, the pole plates and the permanent magnet require an unnecessarily large volume because the defined minimum pole surfaces are required for coupling the permanent magnet. These pole surfaces extend in the longitudinal direction of the relay in front of the coil body flange. Although the contact and pole surfaces of the working air gap are attached at the end face of the pole plate portions which are perpendicular to the coil axis, and thus require little space in the axial direction, the free end of the armature contact tongue which is moveable therebetween requires sufficient space for freedom of movement, so that the permanent magnet must be disposed at a certain distance from the armature contact tongue, thus requiring additional space in the axial direction. The relative positions of the contact and pole surfaces forming the working air gap can be precisely adjusted by adding spacer blocks to the coil body adjacent the contact surfaces. Problems are still present, however, because of the accessibly small air and creep paths between the lengthened portions of the contact surfaces which are disposed opposite each other.
U.S. Pat. No. 4,577,173 describes a relay designed to achieve a relay length which is as small as possible, wherein the pole plates are planar and are placed flat against the end face of the coil body, and a permanent magnet is disposed against the pole plates at the end face with a foil interposed therebetween. The contact surfaces in this relay are disposed at the end faces of respective pole members which are slightly bent or crimped toward the interior of the coil. The contact spacing is defined by additional stop tabs which are cut within the respective pole members and pressed against spacer members of the coil body flange. In order to obtain adequate air and creep paths between these stop tabs, the stop tabs are shortened in comparison to the pole members, thus requiring the spacer members of the coil body flange to have a greater width than the contact distance between the two pole surfaces. In providing for assembly of this relay, however, it has become apparent that maintaining the tolerances between the stop faces of the stop tabs disposed in various planes and the pole surfaces at a small value is very difficult, given a pole surface spacing of a few tenths of a millimeter. Accurately maintaining such tolerances is necessary for a faultless functioning of the relay. These tolerances also have an unfavorable effect for contact spacings within this order of magnitude because the differing material contraction of the plastic used in manufacturing the coil body already contributes a noticeable influence on the spacing members.